A method for producing a yarn for a field of artificial grass

Abstract: A method for producing a yarn for a field of artificial grass by extruding a polymer material into a monofilament, stretching the monofilament at an elevated temperature, relaxing it to obtain a band and twisting several bands together into a yarn, whereby said extrusion takes place via a spinning plate having such a form that monofilaments are obtained, which in the cross-section have regularly spaced-apart protrusions having a height of 10 - 40% of the thickness of the monofilament without protrusions, being a thickness of 100 - 700 µm and a width of 1 - 5 mm, then said stretching takes place at a stretching ratio between 1 : 2 and 1 : 10, whereby bands having a thickness of 50 - 350 µm and a width of 0.5 - 2 mm are obtained after relaxing and cooling, and whereby subsequently 5 - 10 bands are twisted together in order to obtain said yarn.

Description: The invention relates to a method for producing a yarn for a field of artificial grass by extruding a polymer material into a monofilament, stretching the monofilament at an elevated temperature, relaxing it to obtain a band and twisting several bands together into a yarn. A method of this kind is known from EP-A-417,832, wherein a yarn is produced by extruding the granulate and making bands having a width of 2 - 3 mm from the extrusion product, which bands have a width of 1 - 2 mm after stretching, whilst the thickness amounts to 50 - 70% of the original thickness of the extruded bands, whereupon 5 - 10 bands are twisted together into a yarn. It has now become apparent that the mechanical properties of the yarn may be improved by giving the yarn a predetermined form, obtained by extrusion to monofilaments and by stretching them under specific herebelow given circumstances. The method according to the invention is characterized in that said extrusion takes place via a spinning plate having such a form that monofilaments are obtained, which in the cross-section have regularly spaced-apart protrusions having a height of 10 - 40% of the thickness of the monofilament without protrusions, being a thickness of 100 - 700 µm and a width of 1-5 mm, then strectching takes place at a stretching ratio between 1 : 2 and 1 : 10, whereby bands having a thickness of 50 - 350 µm and a width of 0.5 - 2 mm are obtained after relaxing and cooling, and in that subsequently 5 - 10 bands are twisted together in order to obtain said yarn. According to the invention the polymer to be used is preferably a block copolymer consisting of polypropylene and polyethylene marketed by Solvay, Belgium. More in particular the monofilaments have a thickness of 100 - 150 µm and a width of 1 - 1.5 mm after stretching. This is in particular achieved when stretching ratio of 1 : 3-6 is used. The yarn, produced in accordance with EP-A-417,832 has the property that it post fibrillates less than the uptill then known yarns, as result of which the life of the yarn is extended and the field of artificial grass obtained with that yarn can be played on for a longer period of time. The playing-properties can be maintained for a longer period of time, because the field will get less compact by the particles as fibrilated. Another effect achieved by using the method according to the invention is that the yarn will become less sensitive to breaking. This is in particular achieved by giving the cross-section of the yarn a knobby structure, whereby the knobbs are provided in regularly spaced-apart relationship on the monofilaments and thus on the yarn produced from said monofilaments. The invention will be explained in more detail in the following description, wherein reference is made to the appended drawing, which illustrates the cross-section of the extruded monofilament. In Figure 1 the core of the monofilament is indicated at 1 and the protrusions are indicated at 2. The thickness of the monofilament is about 100 µm and the protrusions have a height of 10 - 20 µm. The monofilaments shown in Figure 1 have a width of 1 - 5 mm and the protrusions may preferably be provided on both sides of the monofilament. The invention will be explained in more detail by means of the examples below, whereby it will be apparent that the invention is not limited to these examples. Example 1 An extruder was fed with a block copolymer composed of polyethylene and polypropylene, marketed by Solvay, Belgium, having a melting index of about 4. By using a spinning plate having a large number of apertures several monofilaments as shown in Figure 1 had been produced simultaneously, which monofilaments before stretching have a thickness of 300 µm and a width of 2.8 mm. Said stretching took place at a temperature of 130 °C in a hot air oven at a stretching ratio of 1 : 5 and gave a band having a size of 115 µm thickness and a width of 1.1 mm. For relaxing the bands are reheated by supplying them to rolls having a contact temperature of 155 °C and then cooling them by contacting rolls having a contact temperature of 25 °C, rotating more slowly, so that the bands had been upsetted in a slight way and the sizes of the upsetted bands were a thickness of 125 µm and a width of 1.2 mm. By relaxing, the yarn was less sensitive for shrinking during processes at elevated temperature. From these bands a yarn was then produced by twisting 6 bands. By tufting the said obtained yarn, turf was produced for artificial grass. The field was for hockey having 280 stitches per meter and having a pile height of 25 mm. The thus obtained carpet was subjected to tests in order to determine its mechanical properties. These mechanical properties are in particular determined by means of treadwheel tests. These tests were carried out at 2250 rotations and 5000 rotations and the carpet produced from the yarn obtained according to the invention was compared with the carpet produced from yarn obtained according to European patent application 417,832. The results have been summarized in Table A. Example 2 An extruder was fed with a block copolymer composed of polyethylene and polypropylene as marketed by Solvay, Belgium, which had a melting index of 4. By using a spinning plate comprising a large number of apertures monofilaments as shown in Figure 1 were simultaneously produced, which monofilaments had a thickness of 300 µm and a width of 2.25 mm prior to stretching. Said stretching took place at a temperature of 130 °C in a hot air oven, at a stretching ratio of 1 : 3. After relaxation a band having a width of 1.2 mm and a thickness of 135 µm was obtained. From these bands a yarn was produced by twisting together 8 bands. The yarn thus obtained was made into a field of artificial grass by means of a tufting process. The yarn thus obtained was subjected to tests in order to determine its mechanical properties. These mechanical properties are in particular determined by means of treadwheel tests. These tests were carried at 2250 and 5000 rotations. The results have been summerized in Table A. 2250 rotations 5000 rotations yarn according to EP-A-417,832 2.0% 13.6% yarn according to Example 1 0.6% 3.8% yarn according to Example 2 0.6% 3.75% The carpet obtained from the known yarn already exhibits breakage at 3000 rotations whereas the carpet produced from the yarn according to the invention did not exhibit any sign of pile breakage until 5000 - 7500 rotations. Example 3 The process according to Example 1 was repeated by using pure polypropylene instead of the block copolymer. The results as obtained with the pure polypropylene are the same as the results obtained in Example 1.

Claims: A method for producing a yarn for a field of artificial grass by extruding a polymer material into a monofilament, stretching the monofilament at an elevated temperature, relaxing it to obtain a band and twisting several bands together into a yarn, characterized in that said extrusion takes place via a spinning plate having such a form that monofilaments are obtained, which have in the cross-section regularly spaced-apart protrusions having a height of 10 - 40% of the thickness of the monofilament without protrusions, being a thickness of 100 - 700 µm and a width of 1-5 mm, then said stretching takes place at a stretching ratio between 1 : 2 and 1 : 10, whereby bands having a thickness of 50 - 350 µm and a width of 0.5 - 2 mm are obtained after relaxing and cooling, and in that subsequently 5 - 10 bands are twisted together in order to obtain said yarn. The method according to claim 1, characterized in that the polymer to be used is a block copolymer built up of polypropylene and polyethylene. The method according to claims 1 - 2, characterized in that said monofilaments are stretched to have a thickness of 100 - 150 µm and a width of 1 - 1.5 mm. The method according to claims 1 - 3, characterized in that said stretching ratio is 1 : 3-6. The method according to claims 1 - 4, characterized in that 6 - 9 bands are twisted together into a yarn.

Inventors: GEERTS JAN FRANS MARIE, GEERTS, JAN FRANS MARIE
Applicants: DESSEAUX H TAPIJTFAB, TAPIJTFABRIEK H. DESSEAUX N.V.
Application year: 1994
Main classification: D01D5
IPC codes: D01D5, D02G3, D01F6